CONTROLS ON STONE TEMPERATURES AND THE BENEFITS OF INTERDISCIPLINARY EXCHANGE
J. P. MCGREEVY, P. A. WARKE, & B. J. SMITH
1 1. INTRODUCTION
A number of recent studies at various nationally and internationally important archaeological sites have used microenvironmental data to infer causes of stone deterioration as a basis for formulating conservation strategies (Thorn 1994; Maekawa et al. 1995; Maekawa and Agnew 1996; Thorn and Piper 1996). Underpinning this approach is the view that at any individual site or monument, identification of probable causes of deterioration “demands a more exact knowledge of the environment at the site as well as responses of the monument materials to the environment” (Maekawa et al. 1995, 886).
Because temperature is one of the most significant factors in rock breakdown, operating indirectly through its control on moisture movement and processes such as salt weathering and freeze-thaw and, possibly, directly through “insolation weathering” (structural deterioration of stone by repeated thermally induced expansion and contraction of surface material), attention has inevitably been directed toward stone temperature data in both natural and man-made structures. In the above-mentioned studies, interpretation and discussion of stone temperature data have usually been couched in terms of relationships among such parameters as temperature maxima, minima, ranges, and gradients and what are essentially positional influences such as orientation and inclination of stone surfaces. Occasionally, when more than one stone type is present at the same site, reference has been made to the possibility that, because of differences in thermal properties, different stone types can display dissimilar temperature regimes under similar conditions of exposure (Maekawa et al. 1995). However, the significance of such variations for stone durability is still not fully understood but may have implications for those directly concerned with conservation of stone artifacts and any associated decoration exposed to subaerial conditions.
This article reports a series of field and laboratory experiments that are used to explore the influence of the thermal properties of albedo and conductivity on stone temperature maxima and gradients under a range of ambient conditions. These experiments have been carried out within the subject area of geomorphology, a discipline that, although not specifically related to stone conservation, is, through its concentration on the understanding of weathering processes, of direct relevance to it. Finally, the reported findings are offered in response to a recent call for more interdisciplinary dialogue in matters of common interest (Price 1996).